Tobacco curing system



Aug. 6, 1963 J. F. MOORE TOBACCO CURING SYSTEM Filed Sept. 12, 1960 IN VE N TOR JOHN F. MOORE ay-% 2 ATTORNEYS FIG.1

3,100,145 TOBACCG CURING SYSTEM John F. Moore, 100 Hillsdale Ave. W., Toronto 7, ()ntario, Canada Filed Sept. 12, 1960, Ser. No. 55,277 2 Claims. (CI. 34-48) This invention relates to a system for curing tobacco and, in particular, to a system whereby the temperature and relative humidity of the air within the curing kiln may be controlled. In the curing of tobacco it is customary to hang the tobacco in a building or kiln which is substantially enclosed and sealed.

The interior of the kiln is heated and over a period of time certain chemical and physical changes take place in the tobacco leaves which result in the production of a cured leaf.

The prior art has employed, for many years, a system wherein heat is supplied to the building along the floor thereof, the heated air then rising through the tobacco leaves and escaping through vents sometimes located in the ridge of the roof of the building.

This method or system, although in almost universal usage at the present time, suffers from the disadvantage that as the hot air rises through the cooler tobacco leaves there is a tendency for the hot air to channel or, in other words, to seek the path of least resistance through the tobacco from the source of heat to the vent at the roof of the kiln. As a result the tobacco leaves are unevenly contacted by the Warm air and the curing process is not uniformly carried out.

The present invention proposes to supply the heated air at the top of the kiln and, by means of a closed circuit, forced flow system to drive the heated air downwardly through the tobacco and out through a vent located at or near the bottom of the kiln from which vent it is returned to the circuit after having been reheated.

This concept has the advantage that there is no tendency for the hot air to channel through the tobacco as it moves downwardly and it has been found that the tobacco is uniformly cured by this method.

Specifically, the invention proposes to provide a substantially sealed, enclosed kiln which is provided with a first opening adjacent the top of one wall and a second opening adjacent the bottom of that wall, the openings being joined by a vertically extending duct which en closes a fan and a heat source, the fan driving heated air in a closed circuit through the duct, the first opening at the top of the kiln, downwardly through tobacco within the kiln, and back into the duct through the second open- Means are provided in the duct to admit fresh outside air to the system and means are also provided to exhaust air from the system for purposes which will become apparent as the description proceeds.

The invention is described by way of a preferred embodiment illustrated in the accompanying drawings in which:

FIGURE 1 is a cutaway perspective view of the curing system as attached to the outside of a tobacco kiln, and

FIGURE 2 is a detailed view of a portion of FIG- URE 1.

Referring now to FIGURE 1, a tobacco kiln indicated generally by the reference character may consist of a foundation Wall 11 upon which is constructed a side wall 12 which extends upwardly to a roof portion 13. The tobacco kiln is substantially sealed and enclosed so that there is a minimum of leakage of air into or out of the kiln.

An opening 14 is provided adjacent the top of the wall 12 and a similarly sized opening 15 is positioned verti- 2 cally beneath the opening 14, the opening 14 being hereinafter referred to as the first opening and the opening 15 being hereinafter referred to as the second opening.

The first opening 14 is located in the wall 12 at a level which is at least partly above the uppermost level at which tobacco may be hung in the kiln so that the heated air will enter the kiln above the tobacco. Similarly the second opening 15 is located in the wall 12 at least partly below the lowermost level at which tobacco may be hung so that the air must flow past all of the tobacco before escaping through the opening 15- in the wall 12.

A primary duct :16 of any suitable construction is provided externally of the kiln 16 joining the two openings and within this primary duct 16 is contained the mechanism which is associated with the curing system.

Firstly, there is provided a transverse wall I17 which extends across the primary duct 16 adjacent its lower end and which is provided with a circular central aperture 18 within which is mounted a fan 19 adapted to sweep substantially the entire opening. The periphery of the opening 18 is provided with a flanged collar 20 to define the area swept by the fan 19. The fan 19 is mounted on a substantially vertical shaft 21 which is journaled at 22 on a support member 23 extending diametrically across the opening 118' and positioned below it. A journal 24 is also provided where the shaft 21 passes through the lower Wall 25 of the duct and, at its lower end, the shaft 21 is provided with a pulley 26. An electric motor 27 drives the shaft 21 through a belt 28 which engages the pulley 26 on the shaft 21 and a pulley 29 on the shaft 30 of the motor 27.

Accordingly, it can be seen that rotation of the shaft 21 by the motor 27 will cause the fan 19 to revolve in the direction of the arrow 31 and will drive air through the primary duct 16 in the direction of the arrows 32, through the first opening 14, into the kiln above the uppermost level at which tobacco may be hung, downwardly through the tobacco, and back into the primary duct 16 through the second opening 15.

Below the wall 17 extending across the duct there is provided a source of heat which in the embodiment shown, comprises a secondary duct 33 which extends from the exterior of the primary duct 16 at point 34 across the bottom of the duct in a horizontal direction and then bends upwardly to terminate below the opening 18 in the Wall 17. The interior of the secondary duct 33 is in communication with the outside air at point 34 and at this point a fuel burner 35 is inserted into the end of the secondary duct 33.

Combustion air may enter the secondary duct 33 at the point 34 where it communicates with the outside air and, in addition, an opening 36 is provided in the bottom wall 25 of the primary duct 16 through which outside air may enter the closed circuit. Further openings 37 are provided in the secondary duct 33 so that secondary combustion air may enter the duct 33 at this point from the interior of the duct 16.

Heated air from the secondary duct 33 is discharged upwardly into the opening swept by the fan and into approximately a quadrant of this circular opening 18.

It can be seen, accordingly, that heated air will be driven through the closed circuit described in the direction of the arrows 32 by being forced by means of the fan through the primary duct 16, into the kiln 10 through the first opening 14 above the tobacco and will then pass downwardly through the tobacco and back into the duct through the second opening 15.

Suitable means such as a conventional thermostat 38 will control the burner 35 and will, accordingly, maintain the temperature of the air at a desired level. The thermostat may be controlled by suitable means which are neither shown nor described so that the temperature may either rise over a period of time or fall over a period of time as circumstances may require.

During the curing of tobacco it is not only necessary that the temperature be closely controlled but it is also essential that the humidity of the air within the kiln be controlled. Since the curing of tobacco involves, at certain stages, the removal of moisture from the tobacco leaf, it is necessary to provide means to exhaust some of the moisture laden air from the kiln and to admit outside air, the relative humidity of which 'will be lower than that of the air within the kiln. For this purpose an opening 39 is provided in the wall of the primary duct 16 and this opening is closed by a damper 40 carried by a shaft 41 which is supported in bearings 42 and 43. An arm 44 secured to the shaft 41 and provided with a counter-weight 45 ensures that under normal conditions the damper 40 remains closed.

Connected to the arm 44 is a vertical control rod 46 which, at its lower end 47 is secured to an expandable bellows 48, the interior of which, by means of a conduit 49 is in communication with a bulb 50 contained within an enclosed box 51. The box 51 is located within the primary duct .16 adjacent the second opening 15 and the bulb 50 is provided with a wick 52 which lies over its surface and which hangs into a water bath 53 occupying the lower portion of the box 51. The water bath 53 is maintained at a desired level from a reservoir 54 which may conveniently be mounted externally of the primary duct 16 and connected with the interior of the box 51 by a conduit 55.

The tube 50 contains a material which, under normal circumstances, exerts a substantial vapour pressure which is capable of actuating the bellows 48 and the control rod 46. Such a suitable material is the gas ethyl chloride. The ethyl chloride contained within the tube 50 is in a liquid-vapour phase and the vapour pressure of the material, acting upon the bellows 48 will move the control rod 46 and thereby rotate the shaft 41 to open or close the damper in accordance with predetermined conditions for which the mechanism may have been adjusted.

The box 51 is provided with an opening 56 in its upper surface which opening is in communication with a duct 57 extending vertically inthe primary duct 16 to a point adjacent the first opening 14 where it terminates in an open end 58 to receive air flowing upwardly in the primary duct 16. A second opening 59 is provided in the box 51 at the end thereof remote from the opening 56 so that air flowing upwardlly in the primary duct 16 enters the open end 58, passes downwardly through the duct 57, flows over the water soaked wick 52 lying on the tube 50 and returned to the system through opening 59. Accordingly, the temperature of the material within the tube 50 will be equivalent to the Wet-bulb temperature of the air in the system and the vapour pressure exerted by the ethyl chloride within the tube 50 will be a function of the wet-bulb temperature of the air in the system.

If the wet-bulb temperature of the air becomes too high the vapour pressure of the ethyl chloride will increase and will cause the expansion of the bellows 48 which will cause the control rod -46 to move upwardly as seen in FIGURE 1. This will cause the clockwise rotation of the shaft 41 when viewed in FIGURE 1 which will open the damper and permit a certain amount of the air within the system :to be exhausted through the opening 39. The exhausted humid air will be replaced by fresh, less humid air entering through the opening 36 in the bottom wall 25 of the duct 16 and the over all humidity of the system will thereby be reduced until the wet-bulb temperature of the air within the system has fallen to a value such that the damper 40 may close due to a reduction in the vapour pressure of the ethyl-chloride in the tube 50. It may be seen, therefore, that it is desirable to locate the open end 58 of the tube 57 at such a point that the air it samples has been adequately mixed with whatever fresh air has been admitted and yet has not picked up any moisture from the tobacco in the kiln.

In order to ensure that freshly heated air coming from the secondary duct 33 does not escape through the opening 39 when the damper 40 is open it is to be noted that the upper end 60 of the duct 33 discharges heated air into approximately a quadrant of the opening swept by the fan 19 which 90' quadrant is located substantially diametrically opposed to the opening 39 relative to the opening 18 in the wall 17. Since the fan 19, as seen in FIGURE 1, rotates in a clockwise direction (in the direc tion of the arrow 31), the air will move upwardly through the opening 18 in a clockwise swirl which clockwise swirl will bring the heated air from the secondary duct 33 to a point above the opening 39 by the time it has swung around to a point adjacent the opening 39. Accordingly, freshly heated air coming from the duct 33 will be preserved within the system and there will be a minimum of hot air lost due to the exhausting of the humid air through the opening 39 controlled by the damper 40.

Since the system described is a forced air system there will be a super atmospheric pressure within the kiln 10 which will efiectively prevent the inward leakage of cold outside air into the kiln. Any leakage of air through thekiln walls will be from the inside of the kiln outwardly due to the over pressure which exists within the kiln. As a result there will be no cold air leaking into the kiln to contact the tobacco leaves hanging therein and, accordingly, a substantially uniform temperature may be maintained throughout the entire volume of the kiln which, of course, will promote a uniform curing of the tobacco contained therein.

The construction of the primary duct 16, as stated above, may be of any suitable material such as sheetmetal or composition board. The curing system which has been disclosed is adaptable for use with existing tobacco kilns since the only alterations in those kilns which need be made would be the provision of the first and second openings 14 and 15 and the closing of whatever exit vents may exist within the kiln structure. The device is also, of course, suitable for use in kilns specially designed to receive it and in such cases the construction of the kiln would need to take into account the fact that the invention proposes that the kiln should be enclosed and substantially sealed so as to provide a closed circuit for the forced air system driven by the fan 19.

The source of heat for the secondary duct 33 is shown in the drawing as being a fuel burner. The fuel to be burned maybe natural gas, synthetic gas, oil or any other fuel suitable for such an operation.

Although a specific means has been disclosed for controlling lthe damper 40 in response to the wet-bulb temperature of the air within the system, it is not to be considered that this diclosure is limiting but is merely illustrative of one form which such a control may take. There are other suitable controls which could be used and the invention equally contemplates their use. For example, an electrical sensing element could be used in association with the water soaked wick to control an electrical damper motor operating the damper 40.

As a safety feature, a vane 60 is mounted in the path of air discharged by the fan 19. Air flow from the fan will keep the vane floating or extending in an upward direction from the axis of the shaft 62. In the event that the fan motor. should fail and the air how should cease, the vane 60 will fall and, in doing so, will open electrical contacts in a switch 61 mounted on the end of the shaft 62. This switch 61 would shut off the burner 35 so as to prevent over-heating of the heating unit. It is to be understood that the switch 61 over rides the thermostat control 38-.

It will be seen from the above description that the invention provides an economical, efficient and readily controllable system for curing tobacco wherein the temperature and the relative humidity of the air within the kiln may be closely controlled to achieve the maximum results.

It will be understood that the form of the invention herewith shown and described is a preferred example and various modifications can be carried out without departing from the spirit of the invention or the scope of the appended claims.

What I claim as my invention is:

1. In a tobacco curing system a kiln in which tobacco may be hung for curing, an opening adjacent the lower edge of a Wall of the kiln, a second opening adjacent the upper edge of said Wall, a duct extending between the tWo openings, and air-conditioning mechanism associated with the duct and located at the lower end thereof, and comprising a Wall extending across the duct and having a central circular opening therein, a support member extending diametrically across the said opening and below it, bearings carried by said support member, a shaft journalled in said bearings, and carrying a fan capable of sweeping substantially the entire opening, means to drive said fan, a secondary duet extending from the exterior of the pri mary duct across the bottom of the primary duct and bending upwardly to terminate below said fan, a fuel burner in said secondary duct, means to admit combustion air to the interior of said secondary duct, means responsive to the temperature within the kiln to control the fuel burner, means to admit external air to the duct, damper means to exhaust air from the duct and means responsive to the wet-bulb temperature of the air within the kiln to control the damper means.

2. A tobacco curing system as claimed in claim 1 in which the means responsive to the wet-bulb temperature of the air within the duct includes a duct to bleed air from the circuit and direct it over a wet-bulb, the bulb containing a material in a liquid-vapour phase, the vapour pressure of the material, through the medium of an expanding bellows, actuating mechanism to control the damper.

References Cited in the file of this patent UNITED STATES PATENTS 1,255,350 Tavani Feb. 5, 1918 1,605,634 Wright Nov. 2, 1926 2,286,206 Jackson June 16, 1942 2,288,154 Cobb June 30, 1942 2,608,768 Noel Sept. 2, 1952 FOREIGN PATENTS 48,699 Netherlands June 15, 1940 

1. IN A TOBACCO CURING SYSTEM A KILN IN WHICH TOBACCO MAY BE HUNG FOR CURING, AN OPENING ADJACENT THE LOWER EDGE OF A WALL OF THE KILN, A SECOND OPENING ADJACENT THE UPPER EDGE OF SAID WALL, A DUCT EXENDING BETWEEN THE TWO OPENINGS, AND AIR-CONDITIONING MECHANISM ASSOCIATED WITH THE DUCT AND LOCATED AT THE LOWER END THEREOF, AND COMPRISING A WALL EXTENDING ACROSS THE DUCT AND HAVING A CENTRAL CIRCULAR OPENING THEREIN, A SUPPORT MEMBER EXTENDING DIAMETRICALLY ACROSS THE SAID OPENING AND BELOW IT, BEARINGS CARRIED BY SAID SUPPORT MEMER, A SHAFT JOURNALLED IN SAID BEARINGS, AND CARRYING A FAN CAPABLE OF SWEEPING SUBSTANTIALLY THE ENTIRE OPENING, MEANS TO RIVE SAID FAN, A SECONDARY DUCT EXTENDING FROM THE EXTERIOR OF THE PRIMARY DUCT ACROSS THE BOTTOM OF THE PRIMARY DUCT AND BENDING UPWARDLY TO TERMINATE BELOW SAID FAN, A FUEL BURNER IN SAID SECONDARY DUCT, MEANS TO ADMIT COMBUSTION AIR TO THEINTERIOR OF SAID SECONDARY DUCT, MEANS RESPONSIVE TO THE TEMPERATURE WITHIN THE KILN TO CONTROL THE FUEL BURNER, MEANS TO ADMIT EXTERNAL AIR TO THE DUCT, DAMPER MEANS TO EXHAUST AIR FROM THE DUCT AND MEANS RESPONSIVE TO THE WET-BULB TEMPERATURE OF THE AIR WITHIN HE KILN TO CONTROL THE DAMPER MEANS. 